Method for transmitting and receiving reference signal and apparatus therefor

ABSTRACT

The present disclosure provides a method for receiving a channel state information-reference signal (CSI-RS) by a UE in a wireless communication system. Particularly, the method includes receiving information on a measurement bandwidth and cell list information for a plurality of cells, receiving CSI-RSs of the plurality of cells, and measuring reception power for the CSI-RSs within the measurement bandwidth, wherein sequences of the CSI-RSs are mapped to physical resources based on the same reference position configured by a higher layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/085,161, filed on Sep. 14, 2018, now allowed, which is a NationalStage application under 35 U.S.C. § 371 of International Application No.PCT/KR2018/009180, filed on Aug. 10, 2018, which claims the benefit ofU.S. Provisional Application No. 62/556,513, filed on Sep. 11, 2017, andU.S. Provisional Application No. 62/544,216, filed on Aug. 11, 2017. Thedisclosures of the prior applications are incorporated by reference intheir entirety.

TECHNICAL FIELD

The present disclosure relates to a method for transmitting andreceiving a reference signal and an apparatus therefor, and morespecifically, to a method of setting a reference position for mapping asequence of a CSI-RS (Channel State Information-Reference Signal) and anapparatus therefor.

BACKGROUND ART

As more and more communication devices demand larger communicationtraffic along with the current trends, a future-generation 5^(th)generation (5G) system is required to provide an enhanced wirelessbroadband communication, compared to the legacy LTE system. In thefuture-generation 5G system, communication scenarios are divided intoenhanced mobile broadband (eMBB), ultra-reliability and low-latencycommunication (URLLC), massive machine-type communication (mMTC), and soon.

Herein, eMBB is a future-generation mobile communication scenariocharacterized by high spectral efficiency, high user experienced datarate, and high peak data rate, URLLC is a future-generation mobilecommunication scenario characterized by ultra high reliability, ultralow latency, and ultra high availability (e.g., vehicle to everything(V2X), emergency service, and remote control), and mMTC is afuture-generation mobile communication scenario characterized by lowcost, low energy, short packet, and massive connectivity (e.g., Internetof things (IoT)).traffic according to the current trends, anext-generation 5G system which is a wireless broadband communicationsystem evolving from LTE is required. In such a next-generation 5Gsystem called NewRAT, communication scenarios are divided into enhancedmobile broadband (eMBB), ultra-reliability and low-latency communication(URLLC), massive machine-type communications (mMTC), etc.

DISCLOSURE Technical Problem

An object of the present disclosure is to provide a method fortransmitting and receiving a reference signal and an apparatus therefor.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present disclosure are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present disclosure could achieve will be more clearlyunderstood from the following detailed description.

Technical Solution

A method for receiving a channel state information-reference signal(CSI-RS) by a UE in a wireless communication system according to anembodiment of the present disclosure includes: receiving information ona measurement bandwidth and cell list information for a plurality ofcells; receiving CSI-RSs of the plurality of cells; and measuringreception power for the CSI-RSs within the measurement bandwidth,wherein sequences of the CSI-RSs are mapped to physical resources basedon the same reference position configured by a higher layer.

Here, each of the sequences of the CSI-RSs may be generated based on thesame reference position.

Further, a subcarrier to which the first element of each of thesequences of the CSI-RSs is mapped may be a subcarrier corresponding tothe same reference position.

Further, the method may include reporting information about receptionpower of at least one of the plurality of cells.

Further, each of the sequences of the CSI-RSs may be generated based ona scrambling ID of a corresponding cell configured by the higher layer.

Further, the information on the measurement bandwidth may includeinformation on the starting resource block (RB) of the measurementbandwidth.

A UE receiving a channel state information-reference signal (CSI-RS) ina wireless communication system according to the present disclosureincludes: a transceiver for transmitting/receiving signals to/from abase station; and a processor for controlling the transceiver, whereinthe processor is configured: to control the transceiver to receiveinformation on a measurement bandwidth and cell list information for aplurality of cells and to control the transceiver to receive CSI-RSs ofthe plurality of cells; and to measure reception power for the CSI-RSswithin the measurement bandwidth, wherein sequences of the CSI-RSs aremapped to physical resources based on the same reference positionconfigured by a higher layer.

Here, each of the sequences of the CSI-RSs may be generated based on thesame reference position.

Further, a subcarrier to which the first element of each of thesequences of the CSI-RSs is mapped may be a subcarrier corresponding tothe same reference position.

Further, the processor may control the transceiver to report informationon reception power of at least one of the plurality of cells.

Further, each of the sequences of the CSI-RSs may be generated based ona scrambling ID of a corresponding cell configured by the higher layer.

Further, the information on the measurement bandwidth may includeinformation on the starting resource block (RB) of the measurementbandwidth.

Advantageous Effects

According to the present disclosure, it is possible to alleviate aproblem of collision between CSI-RS sequences due to different BWPs(Bandwidth parts) set for cells.

It will be appreciated by persons skilled in the art that that theeffects that could be achieved with the present disclosure are notlimited to what has been particularly described hereinabove and otheradvantages of the present disclosure will be more clearly understoodfrom the following detailed description taken in conjunction with theaccompanying drawings.

DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating the control-plane and user-planearchitecture of radio interface protocols between a user equipment (UE)and an evolved UMTS terrestrial radio access network (E-UTRAN) inconformance to a 3^(rd) generation partnership project (3GPP) radioaccess network standard.

FIG. 2 is a view illustrating physical channels and a general signaltransmission method using the physical channels in a 3GPP system.

FIG. 3 is a view illustrating a radio frame structure for transmitting asynchronization signal (SS) in a long term evolution (LTE) system.

FIG. 4 is a view illustrating an exemplary slot structure available innew radio access technology (NR).

FIG. 5 is a view illustrating exemplary connection schemes betweentransceiver units (TXRUs) and antenna elements.

FIG. 6 is a view abstractly illustrating a hybrid beamforming structurein terms of TXRUs and physical antennas.

FIG. 7 is a view illustrating beam sweeping for a synchronization signaland system information during downlink (DL) transmission.

FIG. 8 is a view illustrating an exemplary cell in an NR system.

FIGS. 9 to 11 are views illustrating embodiments of setting ameasurement bandwidth.

FIGS. 12 to 14 are views illustrating embodiments of mapping CSI-RSsequences.

FIG. 15 is a block diagram illustrating components of a transmissionapparatus 10 and a reception apparatus 20, for implementing the presentdisclosure.

BEST MODE

The configuration, operation, and other features of the presentdisclosure will readily be understood with embodiments of the presentdisclosure described with reference to the attached drawings.Embodiments of the present disclosure as set forth herein are examplesin which the technical features of the present disclosure are applied toa 3^(rd) generation partnership project (3GPP) system.

While embodiments of the present disclosure are described in the contextof long term evolution (LTE) and LTE-advanced (LTE-A) systems, they arepurely exemplary. Therefore, the embodiments of the present disclosureare applicable to any other communication system as long as the abovedefinitions are valid for the communication system.

The term, Base Station (BS) may be used to cover the meanings of termsincluding remote radio head (RRH), evolved Node B (eNB or eNode B),transmission point (TP), reception point (RP), relay, and so on.

The 3GPP communication standards define downlink (DL) physical channelscorresponding to resource elements (REs) carrying information originatedfrom a higher layer, and DL physical signals which are used in thephysical layer and correspond to REs which do not carry informationoriginated from a higher layer. For example, physical downlink sharedchannel (PDSCH), physical broadcast channel (PBCH), physical multicastchannel (PMCH), physical control format indicator channel (PCFICH),physical downlink control channel (PDCCH), and physical hybrid ARQindicator channel (PHICH) are defined as DL physical channels, andreference signals (RSs) and synchronization signals (SSs) are defined asDL physical signals. An RS, also called a pilot signal, is a signal witha predefined special waveform known to both a gNode B (gNB) and a UE.For example, cell specific RS, UE-specific RS (UE-RS), positioning RS(PRS), and channel state information RS (CSI-RS) are defined as DL RSs.The 3GPP LTE/LTE-A standards define uplink (UL) physical channelscorresponding to REs carrying information originated from a higherlayer, and UL physical signals which are used in the physical layer andcorrespond to REs which do not carry information originated from ahigher layer. For example, physical uplink shared channel (PUSCH),physical uplink control channel (PUCCH), and physical random accesschannel (PRACH) are defined as UL physical channels, and a demodulationreference signal (DMRS) for a UL control/data signal, and a soundingreference signal (SRS) used for UL channel measurement are defined as ULphysical signals.

In the present disclosure, the PDCCH/PCFICH/PHICH/PDSCH refers to a setof time-frequency resources or a set of REs, which carry downlinkcontrol information (DCI)/a control format indicator (CFI)/a DLacknowledgement/negative acknowledgement (ACK/NACK)/DL data. Further,the PUCCH/PUSCH/PRACH refers to a set of time-frequency resources or aset of REs, which carry UL control information (UCI)/UL data/a randomaccess signal. In the present disclosure, particularly a time-frequencyresource or an RE which is allocated to or belongs to thePDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH is referred to as a PDCCHRE/PCFICH RE/PHICH RE/PDSCH RE/PUCCH RE/PUSCH RE/PRACH RE or a PDCCHresource/PCFICH resource/PHICH resource/PDSCH resource/PUCCHresource/PUSCH resource/PRACH resource. Hereinbelow, if it is said thata UE transmits a PUCCH/PUSCH/PRACH, this means that UCI/UL data/a randomaccess signal is transmitted on or through the PUCCH/PUSCH/PRACH.Further, if it is said that a gNB transmits a PDCCH/PCFICH/PHICH/PDSCH,this means that DCI/control information is transmitted on or through thePDCCH/PCFICH/PHICH/PDSCH.

Hereinbelow, an orthogonal frequency division multiplexing (OFDM)symbol/carrier/subcarrier/RE to which a CRS/DMRS/CSI-RS/SRS/UE-RS isallocated to or for which the CRS/DMRS/CSI-RS/SRS/UE-RS is configured isreferred to as a CRS/DMRS/CSI-RS/SRS/UE-RS symbol/carrier/subcarrier/RE.For example, an OFDM symbol to which a tracking RS (TRS) is allocated orfor which the TRS is configured is referred to as a TRS symbol, asubcarrier to which a TRS is allocated or for which the TRS isconfigured is referred to as a TRS subcarrier, and an RE to which a TRSis allocated or for which the TRS is configured is referred to as a TRSRE. Further, a subframe configured to transmit a TRS is referred to as aTRS subframe. Further, a subframe carrying a broadcast signal isreferred to as a broadcast subframe or a PBCH subframe, and a subframecarrying a synchronization signal (SS) (e.g., a primary synchronizationsignal (PSS) and/or a secondary synchronization signal (SSS)) isreferred to as an SS subframe or a PSS/SSS subframe. An OFDMsymbol/subcarrier/RE to which a PSS/SSS is allocated or for which thePSS/SSS is configured is referred to as a PSS/SSS symbol/subcarrier/RE.

In the present disclosure, a CRS port, a UE-RS port, a CSI-RS port, anda TRS port refer to an antenna port configured to transmit a CRS, anantenna port configured to transmit a UE-RS, an antenna port configuredto transmit a CSI-RS, and an antenna port configured to transmit a TRS,respectively. Antenna port configured to transmit CRSs may bedistinguished from each other by the positions of REs occupied by theCRSs according to CRS ports, antenna ports configured to transmit UE-RSsmay be distinguished from each other by the positions of REs occupied bythe UE-RSs according to UE-RS ports, and antenna ports configured totransmit CSI-RSs may be distinguished from each other by the positionsof REs occupied by the CSI-RSs according to CSI-RS ports. Therefore, theterm CRS/UE-RS/CSI-RS/TRS port is also used to refer to a pattern of REsoccupied by a CRS/UE-RS/CSI-RS/TRS in a predetermined resource area.

FIG. 1 illustrates control-plane and user-plane protocol stacks in aradio interface protocol architecture conforming to a 3GPP wirelessaccess network standard between a user equipment (UE) and an evolvedUMTS terrestrial radio access network (E-UTRAN). The control plane is apath in which the UE and the E-UTRAN transmit control messages to managecalls, and the user plane is a path in which data generated from anapplication layer, for example, voice data or Internet packet data istransmitted.

A physical (PHY) layer at layer 1 (L1) provides information transferservice to its higher layer, a medium access control (MAC) layer. ThePHY layer is connected to the MAC layer via transport channels. Thetransport channels deliver data between the MAC layer and the PHY layer.Data is transmitted on physical channels between the PHY layers of atransmitter and a receiver. The physical channels use time and frequencyas radio resources. Specifically, the physical channels are modulated inorthogonal frequency division multiple access (OFDMA) for downlink (DL)and in single carrier frequency division multiple access (SC-FDMA) foruplink (UL).

The MAC layer at layer 2 (L2) provides service to its higher layer, aradio link control (RLC) layer via logical channels. The RLC layer at L2supports reliable data transmission. RLC functionality may beimplemented in a function block of the MAC layer. A packet dataconvergence protocol (PDCP) layer at L2 performs header compression toreduce the amount of unnecessary control information and thusefficiently transmit Internet protocol (IP) packets such as IP version 4(IPv4) or IP version 6 (IPv6) packets via an air interface having anarrow bandwidth.

A radio resource control (RRC) layer at the lowest part of layer 3 (orL3) is defined only on the control plane. The RRC layer controls logicalchannels, transport channels, and physical channels in relation toconfiguration, reconfiguration, and release of radio bearers. A radiobearer refers to a service provided at L2, for data transmission betweenthe UE and the E-UTRAN. For this purpose, the RRC layers of the UE andthe E-UTRAN exchange RRC messages with each other. If an RRC connectionis established between the UE and the E-UTRAN, the UE is in RRCConnected mode and otherwise, the UE is in RRC Idle mode. A Non-AccessStratum (NAS) layer above the RRC layer performs functions includingsession management and mobility management.

DL transport channels used to deliver data from the E-UTRAN to UEsinclude a broadcast channel (BCH) carrying system information, a pagingchannel (PCH) carrying a paging message, and a shared channel (SCH)carrying user traffic or a control message. DL multicast traffic orcontrol messages or DL broadcast traffic or control messages may betransmitted on a DL SCH or a separately defined DL multicast channel(MCH). UL transport channels used to deliver data from a UE to theE-UTRAN include a random access channel (RACH) carrying an initialcontrol message and a UL SCH carrying user traffic or a control message.Logical channels that are defined above transport channels and mapped tothe transport channels include a broadcast control channel (BCCH), apaging control channel (PCCH), a Common Control Channel (CCCH), amulticast control channel (MCCH), a multicast traffic channel (MTCH),etc.

FIG. 2 illustrates physical channels and a general method fortransmitting signals on the physical channels in the 3GPP system.

Referring to FIG. 2, when a UE is powered on or enters a new cell, theUE performs initial cell search (S201). The initial cell search involvesacquisition of synchronization to an eNB. Specifically, the UEsynchronizes its timing to the eNB and acquires a cell identifier (ID)and other information by receiving a primary synchronization channel(P-SCH) and a secondary synchronization channel (S-SCH) from the eNB.Then the UE may acquire information broadcast in the cell by receiving aphysical broadcast channel (PBCH) from the eNB. During the initial cellsearch, the UE may monitor a DL channel state by receiving a DownLinkreference signal (DL RS).

After the initial cell search, the UE may acquire detailed systeminformation by receiving a physical downlink control channel (PDCCH) andreceiving a physical downlink shared channel (PDSCH) based oninformation included in the PDCCH (S202).

If the UE initially accesses the eNB or has no radio resources forsignal transmission to the eNB, the UE may perform a random accessprocedure with the eNB (S203 to S206). In the random access procedure,the UE may transmit a predetermined sequence as a preamble on a physicalrandom access channel (PRACH) (S203 and S205) and may receive a responsemessage to the preamble on a PDCCH and a PDSCH associated with the PDCCH(S204 and S206). In the case of a contention-based RACH, the UE mayadditionally perform a contention resolution procedure.

After the above procedure, the UE may receive a PDCCH and/or a PDSCHfrom the eNB (S207) and transmit a physical uplink shared channel(PUSCH) and/or a physical uplink control channel (PUCCH) to the eNB(S208), which is a general DL and UL signal transmission procedure.Particularly, the UE receives downlink control information (DCI) on aPDCCH. Herein, the DCI includes control information such as resourceallocation information for the UE. Different DCI formats are definedaccording to different usages of DCI.

Control information that the UE transmits to the eNB on the UL orreceives from the eNB on the DL includes a DL/UL acknowledgment/negativeacknowledgment (ACK/NACK) signal, a channel quality indicator (CQI), aprecoding matrix index (PMI), a rank indicator (RI), etc. In the 3GPPLTE system, the UE may transmit control information such as a CQI, aPMI, an RI, etc. on a PUSCH and/or a PUCCH.

FIG. 3 is a diagram illustrating a radio frame structure fortransmitting a synchronization signal (SS) in LTE system. In particular,FIG. 3 illustrates a radio frame structure for transmitting asynchronization signal and PBCH in frequency division duplex (FDD). FIG.3(a) shows positions at which the SS and the PBCH are transmitted in aradio frame configured by a normal cyclic prefix (CP) and FIG. 3(b)shows positions at which the SS and the PBCH are transmitted in a radioframe configured by an extended CP.

An SS will be described in more detail with reference to FIG. 3. An SSis categorized into a primary synchronization signal (PSS) and asecondary synchronization signal (SSS). The PSS is used to acquiretime-domain synchronization such as OFDM symbol synchronization, slotsynchronization, etc. and/or frequency-domain synchronization. And, theSSS is used to acquire frame synchronization, a cell group ID, and/or aCP configuration of a cell (i.e. information indicating whether to anormal CP or an extended is used). Referring to FIG. 4, a PSS and an SSSare transmitted through two OFDM symbols in each radio frame.Particularly, the SS is transmitted in first slot in each of subframe 0and subframe 5 in consideration of a GSM (Global System for Mobilecommunication) frame length of 4.6 ms for facilitation of inter-radioaccess technology (inter-RAT) measurement. Especially, the PSS istransmitted in a last OFDM symbol in each of the first slot of subframe0 and the first slot of subframe 5. And, the SSS is transmitted in asecond to last OFDM symbol in each of the first slot of subframe 0 andthe first slot of subframe 5. Boundaries of a corresponding radio framemay be detected through the SSS. The PSS is transmitted in the last OFDMsymbol of the corresponding slot and the SSS is transmitted in the OFDMsymbol immediately before the OFDM symbol in which the PSS istransmitted. According to a transmission diversity scheme for the SS,only a single antenna port is used. However, the transmission diversityscheme for the SS standards is not separately defined in the currentstandard.

Referring to FIG. 3, by detecting the PSS, a UE may know that acorresponding subframe is one of subframe 0 and subframe 5 since the PSSis transmitted every 5 ms but the UE cannot know whether the subframe issubframe 0 or subframe 5. That is, frame synchronization cannot beobtained only from the PSS. The UE detects the boundaries of the radioframe in a manner of detecting an SSS which is transmitted twice in oneradio frame with different sequences.

Having demodulated a DL signal by performing a cell search procedureusing the PSS/SSS and determined time and frequency parameters necessaryto perform UL signal transmission at an accurate time, a UE cancommunicate with an eNB only after obtaining system informationnecessary for a system configuration of the UE from the eNB.

The system information is configured with a master information block(MIB) and system information blocks (SIBs). Each SIB includes a set offunctionally related parameters and is categorized into an MIB, SIB Type1 (SIB1), SIB Type 2 (SIB2), and SIB3 to SIB8 according to the includedparameters.

The MIB includes most frequently transmitted parameters which areessential for a UE to initially access a network served by an eNB. TheUE may receive the MIB through a broadcast channel (e.g. a PBCH). TheMIB includes a downlink system bandwidth (DL BW), a PHICH configuration,and a system frame number (SFN). Thus, the UE can explicitly knowinformation on the DL BW, SFN, and PHICH configuration by receiving thePBCH. On the other hand, the UE may implicitly know information on thenumber of transmission antenna ports of the eNB. The information on thenumber of the transmission antennas of the eNB is implicitly signaled bymasking (e.g. XOR operation) a sequence corresponding to the number ofthe transmission antennas to 16-bit cyclic redundancy check (CRC) usedin detecting an error of the PBCH.

The SIB1 includes not only information on time-domain scheduling forother SIBs but also parameters necessary to determine whether a specificcell is suitable in cell selection. The UE receives the SIB1 viabroadcast signaling or dedicated signaling.

A DL carrier frequency and a corresponding system bandwidth can beobtained by MIB carried by PBCH. A UL carrier frequency and acorresponding system bandwidth can be obtained through systeminformation corresponding to a DL signal. Having received the MIB, ifthere is no valid system information stored in a corresponding cell, aUE applies a value of a DL BW included in the MIB to a UL bandwidthuntil system information block type 2 (SystemInformationBlockType2,SIB2) is received. For example, if the UE obtains the SIB2, the UE isable to identify the entire UL system bandwidth capable of being usedfor UL transmission through UL-carrier frequency and UL-bandwidthinformation included in the SIB2.

In the frequency domain, PSS/SSS and PBCH are transmitted irrespectiveof an actual system bandwidth in total 6 RBs, i.e., 3 RBs in the leftside and 3 RBs in the right side with reference to a DC subcarrierwithin a corresponding OFDM symbol. In other words, the PSS/SSS and thePBCH are transmitted only in 72 subcarriers. Therefore, a UE isconfigured to detect or decode the SS and the PBCH irrespective of adownlink transmission bandwidth configured for the UE.

Having completed the initial cell search, the UE can perform a randomaccess procedure to complete the accessing the eNB. To this end, the UEtransmits a preamble via PRACH (physical random access channel) and canreceive a response message via PDCCH and PDSCH in response to thepreamble. In case of contention-based random access, it may transmitadditional PRACH and perform a contention resolution procedure such asPDCCH and PDSCH corresponding to the PDCCH.

Having performed the abovementioned procedure, the UE can performPDCCH/PDSCH reception and PUSCH/PUCCH transmission as a general UL/DLsignal transmission procedure.

The random access procedure is also referred to as a random accesschannel (RACH) procedure. The random access procedure is used forvarious usages including initial access, UL synchronization adjustment,resource allocation, handover, and the like. The random access procedureis categorized into a contention-based procedure and a dedicated (i.e.,non-contention-based) procedure. In general, the contention-based randomaccess procedure is used for performing initial access. On the otherhand, the dedicated random access procedure is restrictively used forperforming handover, and the like. When the contention-based randomaccess procedure is performed, a UE randomly selects a RACH preamblesequence. Hence, a plurality of UEs can transmit the same RACH preamblesequence at the same time. As a result, a contention resolutionprocedure is required thereafter. On the contrary, when the dedicatedrandom access procedure is performed, the UE uses an RACH preamblesequence dedicatedly allocated to the UE by an eNB. Hence, the UE canperform the random access procedure without a collision with a differentUE.

The contention-based random access procedure includes 4 steps describedin the following. Messages transmitted via the 4 steps can berespectively referred to as message (Msg) 1 to 4 in the presentinvention.

Step 1: RACH preamble (via PRACH) (UE to eNB)

Step 2: Random access response (RAR) (via PDCCH and PDSCH (eNB to)

Step 3: Layer 2/Layer 3 message (via PUSCH) (UE to eNB)

Step 4: Contention resolution message (eNB to UE)

On the other hand, the dedicated random access procedure includes 3steps described in the following. Messages transmitted via the 3 stepscan be respectively referred to as message (Msg) 0 to 2 in the presentinvention. It may also perform uplink transmission (i.e., step 3)corresponding to PAR as a part of the ransom access procedure. Thededicated random access procedure can be triggered using PDCCH(hereinafter, PDCCH order) which is used for an eNB to indicatetransmission of an RACH preamble.

Step 0: RACH preamble assignment via dedicated signaling (eNB to UE)

Step 1: RACH preamble (via PRACH) (UE to eNB)

Step 2: Random access response(RAR) (via PDCCH and PDSCH) (eNB to UE)

After the RACH preamble is transmitted, the UE attempts to receive arandom access response (RAR) in a preconfigured time window.Specifically, the UE attempts to detect PDCCH (hereinafter, RA-RNTIPDCCH) (e.g., a CRC masked with RA-RNTI in PDCCH) having RA-RNTI (randomaccess RNTI) in a time window. If the RA-RNTI PDCCH is detected, the UEchecks whether or not there is a RAR for the UE in PDSCH correspondingto the RA-RNTI PDCCH. The RAR includes timing advance (TA) informationindicating timing offset information for UL synchronization, UL resourceallocation information (UL grant information), a temporary UE identifier(e.g., temporary cell-RNTI, TC-RNTI), and the like. The UE can performUL transmission (e.g., message 3) according to the resource allocationinformation and the TA value included in the RAR. HARQ is applied to ULtransmission corresponding to the RAR. In particular, the UE can receivereception response information (e.g., PHICH) corresponding to themessage 3 after the message 3 is transmitted.

A random access preamble (i.e. RACH preamble) consists of a cyclicprefix of a length of TCP and a sequence part of a length of TSEQ. TheTCP and the TSEQ depend on a frame structure and a random accessconfiguration. A preamble format is controlled by higher layer. The RACHpreamble is transmitted in a UL subframe. Transmission of the randomaccess preamble is restricted to a specific time resource and afrequency resource. The resources are referred to as PRACH resources. Inorder to match an index 0 with a PRB and a subframe of a lower number ina radio frame, the PRACH resources are numbered in an ascending order ofPRBs in subframe numbers in the radio frame and frequency domain. Randomaccess resources are defined according to a PRACH configuration index(refer to 3GPP TS 36.211 standard document). The RACH configurationindex is provided by a higher layer signal (transmitted by an eNB).

In the LTE/LTE-A system, a subcarrier spacing for a random accesspreamble (i.e., RACH preamble) is regulated by 1.25 kHz and 7.5 kHz forpreamble formats 0 to 3 and a preamble format 4, respectively (refer to3GPP TS 36.211).

Radio Resource Management (RRM) Measurement in LTE

The LTE system supports RRM operation including power control,scheduling, cell search, cell reselection, handover, radio link orconnection monitoring, and connection establishment andre-establishment. In this case, a serving cell may request a UE to sendRRM measurement information corresponding to a measurement value forperforming the RRM operation. In particular, in the LTE system, the UEmay measure cell search information, Reference Signal Received Power(RSRP), Reference Signal Received Quality (RSRQ), and the like for eachcell and then report the measured information. Specifically, in the LTEsystem, the UE receives ‘measConfig’ for RRM measurement from a servingcell through a higher layer signal and then measure RSRP or RSRQaccording to information in ‘measConfig’. The RSRP and RSRQ are definedas follows in TS 36.214.

RSRP: RSRP is defined as the linear average over the power contributions([W]) of the Resource Elements (REs) of Cell-specific Reference Signals(CRSs) transmitted in the measurement frequency bandwidth. For RSRPdetermination, CRS R0 according TS 36.211 may be used. In some cases,CRS R1 may be additionally used to improve reliability. The referencepoint for the RSRP should be an antenna connector of a UE. If receiverdiversity is in use, a reported RSRP value shall not be lower than RSRPof anyone of individual diversities.

RSRQ: RSRQ is defined as N*RSRP/(E-UTRA carrier RSSI), where N is thenumber of RBs in E-UTRA carrier RSSI measurement bandwidth. In thiscase, the measurement of ‘N*RSRP’ and ‘E-UTRA carrier RSSI’ may be madeover the same RB set.

E-UTRA Carrier RSSI is defined as the linear average of the totalreceived power measured only in OFDM symbols containing referencesymbols for antenna port 0 on N RBs obtained from all sources includingco-channel serving and non-serving cells, adjacent channel interference,thermal noise etc.

If higher layer signaling indicates specific subframes for performingRSRP measurement, RSSI is measured over all indicated OFDM symbols. Thereference point for the RSRQ should be an antenna connector of a UE. Ifreceiver diversity is in use, a reported RSRQ value shall not be lowerthan RSRQ of anyone of individual diversities.

RSSI: RSSI means received wide band power including noise and thermalnoise generated within bandwidth defined by a receiver pulse shapingfilter. Even in this case, the reference point for the RSSI should be anantenna connector of a UE. If receiver diversity is in use, a reportedRSSI value shall not be lower than RSSI of anyone of individualdiversities.

Based on the definitions, in the case of intra-frequency measurement, aUE operating in the LTE system is allowed to measure RSRP in bandwidthcorresponding to one of 6, 15, 25, 50, 75, 100 RBs by the allowedmeasurement bandwidth related Information Element (IE) transmitted inSystem Information Block type 3 (SIB3). Meanwhile, in the case ofinter-frequency measurement, the UE is allowed to measure RSRP inbandwidth corresponding to one of 6, 15, 25, 50, 75, 100 RBs by theallowed measurement bandwidth related IE transmitted in SIBS.Alternatively, when there is no IE, the UE may measure RSRP in theentire downlink system frequency band as the default operation. Uponreceiving information on the allowed measurement bandwidth, the UE mayconsider the corresponding value as the maximum measurement bandwidthand then freely measure the RSRP value within the corresponding value.

However, if the serving cell transmits the IE defined as WB-RSRQ andsets the allowed measurement bandwidth equal to or more than 50 RBs, theUE should calculate the RSRP value for the entire allowed measurementbandwidth. Meanwhile, in the case of RSSI, the UE measures RSSI withinthe frequency band of the UE's receiver according to the definition ofRSSI bandwidth.

The NR communication system should provide much better performance thanthe conventional 4G system in terms of data rates, capacity, latency,energy consumption, and costs. In other words, it is necessary tofurther improve the bandwidth, spectral energy, signaling efficiency,and cost-per-bit of the NR system.

Channel State Information (CSI) Report

In LTE, there are two transmission schemes: open-loop MIMO operatingwithout channel information; and closed-loop MIMO operating based onchannel information. Particularly, in closed-loop MIMO, an eNB and a UEmay perform beamforming on the basis of channel state information inorder to obtain a multiplexing gain of MIMO antennas. The eNB transmitsa reference signal to the UE in order to obtain channel stateinformation from the UE and instructs the UE to feed back channel stateinformation measured on the basis of the reference signal through aPUCCH (Physical Uplink Control Channel) or a PUSCH (Physical UplinkShared Channel).

CSI is divided into an RI (Rank Indicator), a PMI (Precoding MatrixIndex) and a CQI (Channel Quality Indication). The RI is rankinformation of a channel, as described above, and indicates the numberof streams that can be received by a UE through the same frequency-timeresource. In addition, the RI is determined by long term fading of thechannel and thus is fed back to an eNB in a longer period than PMI andCQI values.

The PMI is a value which reflects spatial characteristics of a channeland indicates a precoding matrix index of an eNB preferred by a UE onthe basis of metric such as an SINR. Finally, the CQI is a valueindicating a channel intensity and refers to a reception SINR which canbe obtained by an eNB when the eNB uses a PMI.

In an enhanced communication system such as LTE-A, additional multi-userdiversity is obtained using MU-MIMO (multi-user MIMO). Sinceinterference occurs between multiplexed UEs in the antenna domain inMU-MIMO, whether CSI is accurate may affect interference of multiplexedUEs as well as a UE which has reported the CSI. Accordingly, moreaccurate CSI reporting is required in MU-MIMO than in SU-MIMO.

Accordingly, in LTE-A, PMIs are designed in such a manner that a finalPMI is divided into WI, which is a long-term and/or wideband PMI, andW2, which is a short-term and/or sub-band PMI.

As an example of hierarchical codebook transformation which constitutesa final PMI from the aforementioned information W1 and W2, a long-termcovariance matrix of a channel, as represented by Equation 1, may beused.W=norm(W1 W2)  [Equation 1]

In Equation 1, W2 is a short-term PMI and is a codeword of a codebookconfigured to reflect short-term channel information, W is a codeword ofa final codebook, and norm (A) refers to a matrix in which the norm ofeach column of matrix A is normalized to 1.

Specific structures of W1 and W2 are as represented by Equation 2.

$\begin{matrix}{{{W\; 1(i)} = \begin{bmatrix}X_{i} & 0 \\0 & X_{i}\end{bmatrix}},{{where}\mspace{14mu} X_{i}\mspace{14mu}{is}\mspace{14mu}{{Nt}/2}\mspace{14mu}{by}\mspace{14mu} M\mspace{14mu}{{matrix}.}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack \\{{{W\; 2(j)} = {\overset{\overset{r\mspace{14mu}{columns}}{︷}}{\begin{bmatrix}e_{M}^{k} & e_{M}^{l} & \; & e_{M}^{m} \\\; & \; & \ldots & \; \\{\alpha_{j}e_{M}^{k}} & {\beta_{j}e_{M}^{l}} & \; & {\gamma_{j}e_{M}^{m}}\end{bmatrix}}\mspace{14mu}\left( {{{if}\mspace{14mu}{rank}} = r} \right)}},} & \; \\{{{{where}\mspace{14mu} 1} \leq k},l,{m \leq {M\mspace{14mu}{and}\mspace{14mu} k}},l,{m\mspace{14mu}{are}\mspace{14mu}{{integer}.}}} & \;\end{matrix}$

In Equation 2, the codeword has been designed based on correlation ofchannels generated when a cross-polarized antenna is used and an antennaspacing is narrow, for example, when a spacing between neighbor antennasis half a signal wavelength or less. In the case of a cross-polarizedantenna, antennas can be divided into a horizontal antenna group and avertical antenna group. Each antenna group has ULA (uniform lineararray) antenna characteristics and the two antenna groups areco-located.

Accordingly, a correlation between antennas of each group has the samelinear phase increment characteristic and a correlation between antennagroups has a phase rotation characteristic. In conclusion, it isnecessary to design a codebook by reflecting channel characteristicsbecause a codebook contains values obtained by quantizing channels. Forconvenience of description, a rank-1 codeword generated in theabove-described structure may be represented by Equation 3.

$\begin{matrix}{{W\; 1(i)*W\; 2(j)} = \begin{bmatrix}{X_{i}(k)} \\{\alpha_{j}{X_{i}(k)}}\end{bmatrix}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

In Equation 3, the codeword is represented by a vector of the numberN_(T)×1 of Tx antennas and structured as an upper vector X_(i)(k) and alower vector α_(j)X_(i)(k) which respectively indicate correlationcharacteristics of a horizontal antenna group and a vertical antennagroup. It is advantageous to represent X_(i)(k) as a vector having alinear phase increment characteristic by reflecting a correlationbetween antennas of each antenna group, and a DFT matrix may be used asa typical example.

In an enhanced communication system such as LTE-A, additional multi-userdiversity is obtained using MU-MIMO (multi-user MIMO). Sinceinterference occurs between multiplexed UEs in the antenna domain inMU-MIMO, whether CSI is accurate may affect interference of multiplexedUEs as well as a UE which has reported the CSI. Accordingly, moreaccurate CSI reporting is required in MU-MIMO than in SU-MIMO.

In addition, CoMP JT may be regarded as a MIMO system in which antennasare theoretically geographically distributed because a plurality of eNBstransmits the same data to a specific UE in a coordinated manner in CoMPJT. That is, when MU-MIMO is performed in JT, channel state informationwith high accuracy is also required in order to avoid interferencebetween UEs scheduled in a coordinated manner as in single-cell-MU-MIMO.In the case of CoMP CB, accurate channel state information is alsorequired in order to avoid interference applied by a neighbor cell to aserving cell. To increase accuracy of channel state informationfeedback, an additional channel state information feedback report of aUE is required, in general, and the additional channel state informationfeedback report is transmitted to an eNB through a PUCCH or a PUSCH.

Reference Signal

In general, a transmitter transmits an RS known to both the transmitterand a receiver along with data to the receiver so that the receiver mayperform channel measurement in the RS. The RS indicates a modulationscheme for demodulation as well as the RS is used for channelmeasurement. The RS is classified into Dedicated RS (DRS) for a specificUE (i.e. UE-specific RS) and Common RS (CRS) for all UEs within a cell(i.e. cell-specific RS). The cell-specific RS includes an RS in which aUE measures a CQI/PMI/RI to be reported to an eNB. This RS is referredto as Channel State Information-RS (CSI-RS).

OFDM Numerology

A New RAT system adopts an OFDM transmission scheme or a transmissionscheme similar to the OFDM transmission scheme. The New RAT system mayuse different OFDM parameters from LTE OFDM parameters. Or the New RATsystem may follow the numerology of legacy LTE/LTE-A but have a largersystem bandwidth (e.g., 100 MHz). Or one cell may support a plurality ofnumerologies. That is, UEs operating with different numerologies mayco-exist within one cell.

Subframe Structure

In the 3GPP LTE/LTE-A system, a radio frame is 10 ms (307200T_(s)) long,including 10 equal-size subframes (SFs). The 10 SFs of one radio framemay be assigned numbers. T_(s) represents a sampling time and isexpressed as T_(s)=1/(2048*15 kHz). Each SF is 1 ms, including twoslots. The 20 slots of one radio frame may be sequentially numbered from0 to 19. Each slot has a length of 0.5 ms. A time taken to transmit oneSF is defined as a transmission time interval (TTI). A time resource maybe distinguished by a radio frame number (or radio frame index), an SFnumber (or SF index), a slot number (or slot index), and so on. A TTIrefers to an interval in which data may be scheduled. In the currentLTE/LTE-A system, for example, there is a UL grant or DL granttransmission opportunity every 1 ms, without a plurality of UL/DL grantopportunities for a shorter time than 1 ms. Accordingly, a TTI is 1 msin the legacy LTE/LTE-A system.

FIG. 4 illustrates an exemplary slot structure available in the newradio access technology (NR).

To minimize a data transmission delay, a slot structure in which acontrol channel and a data channel are multiplexed in time divisionmultiplexing (TDM) is considered in 5^(th) generation (5G) NR.

In FIG. 4, an area marked with slanted lines represents a transmissionregion of a DL control channel (e.g., PDCCH) carrying DCI, and a blackpart represents a transmission region of a UL control channel (e.g.,PUCCH) carrying UCI. DCI is control information that a gNB transmits toa UE, and may include information about a cell configuration that a UEshould know, DL-specific information such as DL scheduling, andUL-specific information such as a UL grant. Further, UCI is controlinformation that a UE transmits to a gNB. The UCI may include an HARQACK/NACK report for DL data, a CSI report for a DL channel state, ascheduling request (SR), and so on.

In FIG. 4, symbols with symbol index 1 to symbol index 12 may be usedfor transmission of a physical channel (e.g., PDSCH) carrying DL data,and also for transmission of a physical channel (e.g., PUSCH) carryingUL data. According to the slot structure illustrated in FIG. 2, as DLtransmission and UL transmission take place sequentially in one slot,transmission/reception of DL data and reception/transmission of a ULACK/NACK for the DL data may be performed in the one slot. As aconsequence, when an error is generated during data transmission, a timetaken for a data retransmission may be reduced, thereby minimizing thedelay of a final data transmission.

In this slot structure, a time gap is required to allow a gNB and a UEto switch from a transmission mode to a reception mode or from thereception mode to the transmission mode. For the switching between thetransmission mode and the reception mode, some OFDM symbol correspondingto a DL-to-UL switching time is configured as a guard period (GP) in theslot structure.

In the legacy LTE/LTE-A system, a DL control channel is multiplexed witha data channel in TDM, and a control channel, PDCCH is transmitteddistributed across a total system band. In NR, however, it is expectedthat the bandwidth of one system will be at least about 100 MHz, whichmakes it inviable to transmit a control channel across a total band. Ifa UE monitors the total band to receive a DL control channel, for datatransmission/reception, this may increase the battery consumption of theUE and decrease efficiency. Therefore, a DL control channel may betransmitted localized or distributed in some frequency band within asystem band, that is, a channel band in the present disclosure.

In the NR system, a basic transmission unit is a slot. A slot durationincludes 14 symbols each having a normal cyclic prefix (CP), or 12symbols each having an extended CP. Further, a slot is scaled in time bya function of a used subcarrier spacing. That is, as the subcarrierspacing increases, the length of a slot decreases. For example, given 14symbols per slot, if the number of slots in a 10-ms frame is 10 for asubcarrier spacing of 15 kHz, the number of slots is 20 for a subcarrierspacing of 30 kHz, and 40 for a subcarrier spacing of 60 kHz. As thesubcarrier spacing increases, the length of an OFDM symbol decreases.The number of OFDM symbols per slot is different depending on the normalCP or the extended CP, and does not change according to a subcarrierspacing. The basic time unit for LTE, T_(s) is defined as 1/(15000*2048)seconds, in consideration of the basic 15-kHz subcarrier spacing and amaximum FFT size of 2048. T_(s) is also a sampling time for the 15-kHzsubcarrier spacing. In the NR system, many other subcarrier spacingsthan 15 kHz are available, and since a subcarrier spacing is inverselyproportional to a corresponding time length, an actual sampling timeT_(s) corresponding to subcarrier spacings larger than 15 kHz becomesshorter than 1/(15000*2048) seconds. For example, the actual samplingtime for the subcarrier spacings of 30 kHz, 60 kHz, and 120 kHz may be1/(2*15000*2048) seconds, 1/(4*15000*2048) seconds, and 1/(8*15000*2048)seconds, respectively.

Analog Beamforming

For a 5G mobile communication system under discussion, a technique ofusing an ultra-high frequency band, that is, a millimeter frequency bandat or above 6 GHz is considered in order to transmit data to a pluralityof users at a high transmission rate in a wide frequency band. The 3GPPcalls this technique NR, and thus a 5G mobile communication system willbe referred to as an NR system in the present disclosure. However, themillimeter frequency band has the frequency property that a signal isattenuated too rapidly according to a distance due to the use of toohigh a frequency band. Accordingly, the NR system using a frequency bandat or above at least 6 GHz employs a narrow beam transmission scheme inwhich a signal is transmitted with concentrated energy in a specificdirection, not omni-directionally, to thereby compensate for the rapidpropagation attenuation and thus overcome the decrease of coveragecaused by the rapid propagation attenuation. However, if a service isprovided by using only one narrow beam, the service coverage of one gNBbecomes narrow, and thus the gNB provides a service in a wideband bycollecting a plurality of narrow beams.

As a wavelength becomes short in the millimeter frequency band, that is,millimeter wave (mmW) band, it is possible to install a plurality ofantenna elements in the same area. For example, a total of 100 antennaelements may be installed at (wavelength) intervals of 0.5 lamda in a30-GHz band with a wavelength of about 1cm in a two-dimensional (2D)array on a 5 by 5 cm panel. Therefore, it is considered to increasecoverage or throughput by increasing a beamforming gain through use of aplurality of antenna elements in mmW.

To form a narrow beam in the millimeter frequency band, a beamformingscheme is mainly considered, in which a gNB or a UE transmits the samesignals with appropriate phase differences through multiple antennas, tothereby increase energy only in a specific direction. Such beamformingschemes include digital beamforming for generating a phase differencebetween digital baseband signals, analog beamforming for generating aphase difference between modulated analog signals by using a time delay(i.e., a cyclic shift), and hybrid beamforming using both digitalbeamforming and analog beamforming. If a TXRU is provided per antennaelement to enable control of transmission power and a phase per antenna,independent beamforming per frequency resource is possible. However,installation of TXRUs for all of about 100 antenna elements is noteffective in terms of cost. That is, to compensate for rapid propagationattenuation in the millimeter frequency band, multiple antennas shouldbe used, and digital beamforming requires as many RF components (e.g.,digital to analog converters (DACs), mixers, power amplifiers, andlinear amplifiers) as the number of antennas. Accordingly,implementation of digital beamforming in the millimeter frequency bandfaces the problem of increased cost of communication devices. Therefore,in the case where a large number of antennas are required as in themillimeter frequency band, analog beamforming or hybrid beamforming isconsidered. In analog beamforming, a plurality of antenna elements aremapped to one TXRU, and the direction of a beam is controlled by ananalog phase shifter. A shortcoming with this analog beamforming schemeis that frequency selective beamforming (BF) cannot be provided becauseonly one beam direction can be produced in a total band. Hybrid BFstands between digital BF and analog BF, in which B TXRUs fewer than Qantenna elements are used. In hybrid BF, the directions of beamstransmittable at the same time is limited to or below B although thenumber of beam directions is different according to connections betweenB TXRUs and Q antenna elements.

FIG. 5 is a view illustrating exemplary connection schemes between TXRUsand antenna elements.

(a) of FIG. 5 illustrates connection between a TXRU and a sub-array. Inthis case, an antenna element is connected only to one TXRU. Incontrast, (b) of FIG. 5 illustrates connection between a TXRU and allantenna elements. In this case, an antenna element is connected to allTXRUs. In FIG. 5, W represents a phase vector subjected tomultiplication in an analog phase shifter. That is, a direction ofanalog beamforming is determined by W. Herein, CSI-RS antenna ports maybe mapped to TXRUs in a one-to-one or one-to-many correspondence.

As mentioned before, since a digital baseband signal to be transmittedor a received digital baseband signal is subjected to a signal processin digital beamforming, a signal may be transmitted or received in orfrom a plurality of directions on multiple beams. In contrast, in analogbeamforming, an analog signal to be transmitted or a received analogsignal is subjected to beamforming in a modulated state. Thus, signalscannot be transmitted or received simultaneously in or from a pluralityof directions beyond the coverage of one beam. A gNB generallycommunicates with multiple users at the same time, relying on thewideband transmission or multiple antenna property. If the gNB usesanalog BF or hybrid BF and forms an analog beam in one beam direction,the gNB has no way other than to communicate only with users covered inthe same analog beam direction in view of the nature of analog BF. Alater-described RACH resource allocation and gNB resource utilizationscheme according to the present invention is proposed by reflectinglimitations caused by the nature of analog BF or hybrid BF.

Hybrid Analog Beamforming

FIG. 6 abstractly illustrates a hybrid beamforming structure in terms ofTXRUs and physical antennas.

For the case where multiple antennas are used, hybrid BF with digital BFand analog BF in combination has emerged. Analog BF (or RF BF) is anoperation of performing precoding (or combining) in an RF unit. Due toprecoding (combining) in each of a baseband unit and an RF unit, hybridBF offers the benefit of performance close to the performance of digitalBF, while reducing the number of RF chains and the number of DACs (oranalog to digital converters (ADCs). For the convenience' sake, a hybridBF structure may be represented by N TXRUs and M physical antennas.Digital BF for L data layers to be transmitted by a transmission end maybe represented as an N-by-N matrix, and then N converted digital signalsare converted to analog signals through TXRUs and subjected to analog BFrepresented as an M-by-N matrix. In FIG. 6, the number of digital beamsis L, and the number of analog beams is N. Further, it is considered inthe NR system that a gNB is configured to change analog BF on a symbolbasis so as to more efficiently support BF for a UE located in aspecific area. Further, when one antenna panel is defined by N TXRUs andM RF antennas, introduction of a plurality of antenna panels to whichindependent hybrid BF is applicable is also considered. As such, in thecase where a gNB uses a plurality of analog beams, a different analogbeam may be preferred for signal reception at each UE. Therefore, a beamsweeping operation is under consideration, in which for at least an SS,system information, and paging, a gNB changes a plurality of analogbeams on a symbol basis in a specific slot or SF to allow all UEs tohave reception opportunities.

FIG. 7 is a view illustrating beam sweeping for an SS and systeminformation during DL transmission. In FIG. 7, physical resources or aphysical channel which broadcasts system information of the New RATsystem is referred to as an xPBCH. Analog beams from different antennapanels may be transmitted simultaneously in one symbol, and introductionof a beam reference signal (BRS) transmitted for a single analog beamcorresponding to a specific antenna panel as illustrated in FIG. 7 isunder discussion in order to measure a channel per analog beam. BRSs maybe defined for a plurality of antenna ports, and each antenna port ofthe BRSs may correspond to a single analog beam. Unlike the BRSs, the SSor the xPBCH may be transmitted for all analog beams included in ananalog beam group so that any UE may receive the SS or the xPBCHsuccessfully.

FIG. 8 is a view illustrating an exemplary cell in the NR system.

Referring to FIG. 8, compared to a wireless communication system such aslegacy LTE in which one eNB forms one cell, configuration of one cell bya plurality of TRPs is under discussion in the NR system. If a pluralityof TRPs form one cell, even though a TRP serving a UE is changed,seamless communication is advantageously possible, thereby facilitatingmobility management for UEs.

Compared to the LTE/LTE-A system in which a PSS/SSS is transmittedomni-directionally, a method for transmitting a signal such as aPSS/SSS/PBCH through BF performed by sequentially switching a beamdirection to all directions at a gNB applying mmWave is considered. Thesignal transmission/reception performed by switching a beam direction isreferred to as beam sweeping or beam scanning. In the presentdisclosure, “beam sweeping” is a behavior of a transmission side, and“beam scanning” is a behavior of a reception side. For example, if up toN beam directions are available to the gNB, the gNB transmits a signalsuch as a PSS/SSS/PBCH in the N beam directions. That is, the gNBtransmits an SS such as the PSS/SSS/PBCH in each direction by sweeping abeam in directions available to or supported by the gNB. Or if the gNBis capable of forming N beams, the beams may be grouped, and thePSS/SSS/PBCH may be transmitted/received on a group basis. One beamgroup includes one or more beams. Signals such as the PSS/SSS/PBCHtransmitted in the same direction may be defined as one SS block (SSB),and a plurality of SSBs may exist in one cell. If a plurality of SSBsexist, an SSB index may be used to identify each SSB. For example, ifthe PSS/SSS/PBCH is transmitted in 10 beam directions in one system, thePSS/SSS/PBCH transmitted in the same direction may form an SSB, and itmay be understood that 10 SSBs exist in the system. In the presentdisclosure, a beam index may be interpreted as an SSB index.

Hereinafter, a method for transmitting and receiving a reference signal,particularly, a CSI-RS according to the present disclosure will bedescribed.

Downlink Reference Signal for RRM Measurement

A fixed value is used as a power offset of an SSS with respect to a PBCHDM-RS. Here, to determine the fixed value, it is necessary to determinehow resource elements (REs) that are not used for an SS and a PBCHincluding a PSS/SSS will be used in symbols to which SSBs are mapped.

That is, if null REs of SSBs are not used for other channels, it isdesirable to use power for the REs to increase Tx power of the SS. Here,the power offset of the SSS with respect to the PBCH DM-RS may bedetermined as 3.5 dB if any other methods such as PBCH DM-RS powerboosting are not considered. However, the null REs of the SSBs areregarded as resources for other channels and power boosting for the SSis an issue with respect to implementation, and thus it is desirable todetermine the power offset value of the SSS with respect to the PBCHDM-RS as 0 dB.

Here, the number of null REs in the SSBs is 288, which are sufficientfor use as resources for REs for a PDSCH and various channels such as apaging indicator. Accordingly, null REs may be used for transmission ofa specific channel and the power offset of the SSS with respect to thePBCH DM-RS may be fixed to 0 dB. In this case, power increase of the SSfor coverage improvement may remain an issue in implementation of agNodeB.

Definition of RSRP and RSRQ 1. Definition of RSRP

RSRP is measured on the basis of a CRS in LTE, whereas RSRP is measuredusing the SS and the PBCH DM-RS in the NR system. Definition of RSRP isshown in Table 1.

TABLE 1 Definition Reference signal received power (RSRP), is defined asthe linear average over the power contributions (in [W]) of the resourceelements that carry secondary synchronization signals within theconsidered measurement frequency bandwidth. For RSRP determination, thesecondary synchronization signals according to 3GPP TS 38.211 [4] shallbe used. UE may use demodulation reference signals for physicalbroadcast channel in addition to secondary synchronization signal todetermine RSRP. RSRP per cell shall be derived by the UE by linearaveraging over best N RSRP above absolute configured threshold. [Thereference point for the RSRP shall be the antenna connector of the UE[If receiver diversity is in use by the UE, the reported value shall notbe lower than the corresponding RSRP of any of the individual diversitybranches.]

The contents of Table 1 are described in detail hereinafter.

(1) RSRP of SSS or PBCH DM-RS

SS/PBCH RSRP may be measured through the SSS and PBCH DM-RS and a signalactually used to measure the SS/PBCH RSRP is an issue of implementation.However, it is necessary to define at least whether a reported value ismeasured on the basis of the SSS or the PBCH DM-RS. Since the PBCH DM-RSis considered as an assistance signal of the SSS, actual SSS RSRP isused as SS/PBCH RSRP and PBCH DM-RS RSRP needs to be compensated with apower offset value for obtaining SS/PBCH RSRP.

(2) Whether RSRP is Measured at Beam Level or Cell Level

In the NR system, RSRP is measured at a beam level first and cell-levelRSRP is calculated on the basis of beam-level RSRP and reported. Thatis, cell quality may be obtained by selecting up to N−1 best beamshaving quality equal to or higher than a threshold value set as anabsolute value and calculating the average of N−1 or fewer best beams.Accordingly, it is sufficient to define only RSRP measurement withrespect to the beam level in a physical layer.

(3) Antenna Connector

In the NR system, a diversity branch, that is, a receiver antenna port,may be composed of a plurality of antenna elements for analogbeamforming and a measurement point according thereto needs to beaccurately designated. Further, when a maximum coupling loss (MCL) orchannel quality of a UE is discussed, an antenna gain may include abeamforming gain. Accordingly, a diversity branch, that is, an antennaconnector for a measurement point, needs to be defined as a positionafter completion of analog beamforming.

2. Definition of RSSI and RSRP

Although RSRQ is simply defined as RSRP/RSSI in a linear domain, onlythe RSSI is defined in the present invention. If no configuration isused, the RSSI may be measured only through all REs included in an SSblock for RSRP measurement. However, when beams are coordinated orscheduling between cells or TRPs is adjusted in a multi-beam scenario,REs for RSSI measurement may be designated by a network and a UE needsto measure RSSI using OFDM symbols configured by a gNodeB. Here, REs forRSSI measurement may be beam-specific or beam-common.

Configuration for SSB-Based Measurement 1. Configuration for SSB-BasedMeasurement

Parameters which can be basically configured for SSB-based measurementinclude a measurement duration, a period and a slot offset from a frameboundary. Thereamong, the number of measurement periods may be set to amaximum of 2 for intra-frequency measurement or set to a maximum of 1for idle mode or inter-frequency measurement. A measurement period andan offset from a frame boundary need to be set such that all SSBs ofcells included in a cell list or a target cell are transmitted within aconfigured measurement window. If there are multiple measurementperiods, measurement opportunity between configured windows may beconfigured per cell.

2. Actual Transmitted SSB

Information about actual transmitted SSBs needs to be configured inconsideration of UE complexity in addition to parameters which can bebasically set. In addition, information about actual transmitted SSBs ofa neighbor cell may be information about subset measurement of candidateSSBs.

In the case of an idle mode, information about actual transmitted SSBsof a neighboring cell is transmitted to UEs as a configuration parameterof SSB-based measurement. Further, when configuration per cell is notconsiderable from the viewpoint of signaling overhead, the informationabout actual transmitted SSBs may be configured along with a defaultvalue per frequency for cells which are not included in the cell list,and information about actual transmitted SSBs of the serving cell may beadditionally configured for optimization of serving cell operation. Inthe case of a connected mode, information configured in the idle modemay be used as a default value and additional information may beconfigured along with a measurement period per cell for both the servingcell and neighbor cells.

For the serving cell, the information about actually transmitted SSBsneeds to be configured as full bitmap information for correct ratematching of a PDSCH as well as optimization of measurement operation.For example, if the number of SSBs that can be transmitted is 64, theinformation needs to be configured as 64-bit bitmap information.

On the other hand, configuration per cell with respect to neighbor cellsrequires a large amount of signaling messages and thus needs to betransmitted in a compressed form in order to minimize signalingoverhead. Further, a basic configuration for actual transmitted SSBs isrequired for cells which are not included in the cell list in additionto configurations per cell.

CSI-RS Resource and Measurement Configuration

Design of a CSI-RS for RRM measurement is the same as a CSI-RS for beammanagement. That is, basic resource configuration for RRM measurement,such as port number, resource density, number of OFDM symbols perCSI-RS, and whether a CSI-RS is configurable, may be determinedaccording to the CSI-RS for beam management. Meanwhile, RRM measurementrelated parameters other than the aforementioned CSI-RS resourceconfiguration will be described later.

1. Periodicity

A basic characteristic for L3 mobility is determining CSI-RSperiodicity, that is, whether a CSI-RS is transmitted periodically oraperiodically. When the CSI-RS is triggered in an aperiodic manner,downlink control overhead occurs. In addition, it is not easy todynamically trigger CSI-RS transmission of a neighbor cell for L3mobility. Accordingly, the CSI-RS for L3 mobility needs to beperiodically transmitted in consideration of UE operation of L3mobility.

In a discussion about SSB periodicity for mobility, an SSB period is setto {5 ms, 10 ms, 20 ms, 40 ms, 80 ms, 160 ms}. In addition, the CSI-RSis used as a complementary RS for SSBs in order to support stabilizedmobility when SSBs have a more segmented beam level while having longerperiodicity. Accordingly, a CSI-RS transmission period may need not belonger than an SSB transmission period and thus {5 ms, 10 ms, 20 ms, 40ms} may be used as CSI-RS periods for RRM measurement. In addition, ameasurement period may be configured per resource according to CSI-RSresource configuration of a UE dedicated signaling message for at leastintra-frequency measurement.

2. Configuration of Different Bandwidths and Center Frequencies forCells

In the NR system, an eNB supports frequency bands of a wideband with onecomponent carrier (CC) in order to improve frequency efficiency. In thiscase, the eNB supports wideband frequencies, but UEs may have differentradio frequencies (RFs) or processing capabilities and differentfrequency bands may be required according to services and thus the eNBneeds to be able to simultaneously support UEs operating in differentfrequency bands at a wideband frequency. Here, a frequency bandconfigured to support services per UE may be referred to as a bandwidthpart (BWP) and the BWP may be configured by parameters different forrespective UEs.

In addition, when a plurality of narrow band UEs is supported in awideband, BWPs may be configured at different frequency positions forUEs in order to disperse data loads or support different subcarrierspacings (SCSs). Here, frequency bands which are not used may be presentin the entire wideband, and an eNB may not transmit signals through theunused frequency bands in order to increase power efficiency and toreduce the amount of interference with respect to neighbor cells.

Furthermore, an eNB may configure different bandwidths for cells foroptimization of costs because a data load may be different in regions.When the above-described configuration is applied to each eNB, differentbandwidths and center frequencies may be configured for cells, as shownin FIGS. 9 to 11.

3. Measurement Bandwidth

In LTE, a CRS is used for RRM measurement and a system bandwidth of aneighbor cell may differ from that of a serving cell, and a measurementbandwidth for RRM measurement of the CRS is configured. In addition,even though a UE satisfies minimum performance requirements, the UE maysufficiently use the CRS for the configured measurement bandwidth inorder to minimize UE complexity.

Meanwhile, in the NR system, a CSI-RS measurement bandwidth to beapplied to all neighbor cells may be configured through a UE dedicatedRRC configuration message using the same strategy as in LTE and may becommonly applied to all CSI-RS resources. From the viewpoint of UEs,CSI-RS measurement bandwidth information configured through the UEdedicated RRC configuration message refers to a maximum measurementbandwidth permitted for CSI-RS measurement, and an actual amount of partof the CSI-RS bandwidth used for measurement by UEs is an issue ofimplementation. For example, a maximum measurement bandwidth permittedfor CSI-RS measurement may be configured in the range of 5 to 100 MHz atbelow 6 GHz and in the range of 50 to 400 MHz at above 6 GHz.

Further, a frequency position of a measurement band needs to be definedin addition to the measurement bandwidth. In addition, definition ofintra-frequency and inter-frequency measurement for the frequencyposition of the measurement band is as follows.

1) Intra-frequency measurement: A UE may be configured to performintra-frequency measurement for SSBs and/or CSI-RS resources. SSB-basedintra-frequency measurement and CSI-RS-based intra-frequency measurementare defined as follows.

In SSB-based measurement performed by the UE for a neighbor cell, acenter frequency of an SSB used for measurement of a serving cell isidentical to a center frequency of an SSB used for measurement of theneighbor cell.

CSI-RS-based measurement performed by the UE in the neighbor cell iscalled intra-frequency measurement provided by a center frequency of aCSI-RS resource configured for measurement of the serving cell. Here,the center frequency of the CSI-RS resource configured for measurementof the serving cell is identical to a center frequency of a CSI-RSconfigured for measurement in the neighbor cell.

2) Inter-frequency measurement: A UE may be configured to performinter-frequency measurement for SSBs and/or CSI-RS resources. SSB-basedinter-frequency measurement and CSI-RS-based inter-frequency measurementare defined as follows.

In SSB-based measurement performed by the UE in a neighbor cell, acenter frequency of an SSB used for measurement of a serving cell isdifferent from a center frequency of an SSB used for measurement of theneighbor cell.

CSI-RS-based measurement performed by the UE in the neighbor cell iscalled intra-frequency measurement provided by a center frequency of aCSI-RS resource configured for measurement of the serving cell. Here,the center frequency of the CSI-RS resource configured for measurementof the serving cell is different from a center frequency of a CSI-RSconfigured for measurement in the neighbor cell.

3) A scenario for a plurality of SSBs in a serving cell: When a servingcell of a UE transmits a plurality of SS blocks, the UE needs toconfigure a reference SSB in the serving cell in order to performSSB-based intra-frequency measurement.

If a measurement band is located outside an active BWP, this correspondsto inter-frequency measurement. Accordingly, CSI-RS-based measurement isonly considered when the measurement band is located within the activeBWP. Hence, when a measurement bandwidth is less than the active BWP,the frequency position of the measurement band is signaled to the UE.Here, information on the frequency position of the measurement band issignaled to the UE as a starting RB position within the active BWP.However, if the measurement bandwidth is identical to the active BWP,starting RB positions thereof are identical and thus the frequencyposition information of the measurement band may be omitted.

The aforementioned CSI-RS measurement bandwidth configuration isdescribed in more detail hereinafter.

In a mobile communication system, signal qualities of neighbor cells aswell as a serving cell are measured and reported to an eNB in order tosupport mobility. Then, the eNB determines a serving cell on the basisof the signal qualities and signals the serving cell to UEs. To thisend, a UE may measure signal quality using a signal transmitted in asystem bandwidth defined by the system, in general, as shown in FIG. 9.

In systems such as LTE and NR, however, a plurality of bandwidths isdefined in the standards and different frequency bands may be configuredfor cells within a frequency band operated by one operator. Accordingly,if the center frequencies of system bands for all cells are identicalalthough different bandwidths are configured for cells within a systembandwidth operated by an operator, an eNB needs to signal, to UE,information about a measurement bandwidth in which signal qualities ofall cells in which the eNB is interested can be measured, as shown inFIG. 10. Here, the center frequency of the measurement bandwidth may beconfigured to be identical to the center frequency of the systembandwidth, as shown in FIG. 10.

Additionally, when different bandwidths are configured for cells withinthe system bandwidth operated by the operator and center frequencies forthe cells also different within the system bandwidth, that is, when ameasurement bandwidth is less than the active BWP, the eNB may signal,to UEs, information about the position of the measurement bandwidth inthe active BWP along with information about the measurement bandwidth,as shown in FIG. 11. More specifically, referring to FIG. 11, theposition of the measurement bandwidth may be signaled using a relativeposition of the starting frequency or the starting RB of the measurementBWP with respect to the starting frequency or the starting RB of theactive BWP, that is, an offset value. However, when a measurement bandincludes the entire active BWP, the size of the active BWP is identicalto the size of the measurement bandwidth and thus transmission ofinformation about the active BWP may be omitted. That is, if theinformation about the active BWP is not additionally configured, a UEmay perform measurement of a mobility RS on the assumption that theactive BWP is configured as a measurement bandwidth.

4. Numerology of CSI-RS

Although a subcarrier spacing of the CSI-RS is based on a subcarrierspacing of a data channel for facilitation of resource allocation, ingeneral, a subcarrier spacing of a data channel of a neighbor cell maynot be identical to the subcarrier spacing of a data channel of aserving cell. Accordingly, the subcarrier spacing of the CSI-RS may besemi-statically configured per cell or frequency through an RRCconfiguration message. However, configuration of the subcarrier spacingof the CSI-RS per frequency may be preferable in terms of UE complexity.In addition, measurement with respect to cells having differentsubcarrier spacings corresponds to inter-frequency measurement, asdescribed above. Accordingly, the subcarrier spacing of the CSI-RS maybe configured per frequency or measurement object.

That is, a symbol duration of the CSI-RS is based on a subcarrierspacing of a data channel and is configured per frequency through an RRCsignaling message. Here, a subcarrier spacing of a data channel may be{15, 30, 60 kHz} at below 6 GHz and may be {60, 120 kHz} at above 6 GHz.

5. Resource Configuration and RE Mapping

In intra-frequency measurement, information about CSI-RS resources maybe configured per resource for efficient use of resources and needs tobe configured as time and frequency resource information. Informationabout time resources may be provided as information about absolutesymbol positions on the basis of SFN, frame and slot boundaryinformation about each target cell determined by SSB timing information.In addition, information about frequency resources is configured as astarting RB position in a BWP, and as an RE density and an RE positionin an RB. Here, cases in which a starting RB position in a BWP is setmay be limited to cases in which a measurement bandwidth is less thanthe bandwidth of an active BWP and cases in which RE density isconfigured may be limited to cases in which RE density is not fixed instandard documents.

Furthermore, time information about CSI-RS resources may be based onSFN, frame and slot boundary information, as described above. Here, thetime information may be acquired by decoding a PBCH transmitted in afrequency band of 6 GHz or higher.

However, in the case of inter-frequency measurement, HARQ cannot becompletely combined due to measurement gap configuration and thus PBCHdecoding performance cannot be guaranteed. Accordingly, a UE cannotdetermine symbol positions with respect to CSI-RS resources irrespectiveCSI-RS resource configuration unless CSI-RS resources are limited withinsymbols with respect to QCLed SSBs. Therefore, CSI-RS-based RRMmeasurement may be permitted only when time resources for the CSI-RS areconfigured in symbols of QCLed SSBs in inter-frequency measurement andCSI-RS-based RRM measurement is not configured at above 6 GHz if not.

6. Contents of QCL Information and Measurement Report

The CSI-RS does not have a self-synchronization property and requires aphysical cell ID to obtain temporal positions of CSI-RS resources. Inaddition, the SSB may aid in mitigating UE complexity for RRMmeasurement and thus it is desirable that spatial QCL information aboutthe SSB be provided as a configuration parameter. That is, SSB andCSI-RS resources are spatially QCLed for timing synchronization in QCLinformation and the QCL information needs to include information about aPCID. Such QCL information needs to be configured per resource.

The contents of a measurement report may depend on whether the CSI-RS isassociated with the SSB. For example, if the CSI-RS is associated withthe SSB when a CSI-RS RSRP based measurement event is triggered, SSBRSRP may be reported along with CSI-RS RSRP. However, if the CSI-RS isnot associated with the SSB, a UE need not report the SSB when reportingCSI-RS RSRP. Further, when CSI-RS resources are not configured for aspecific cell, only SSB RSRP may be reported to the specific cell.

7. Parameters of Mobility Reference Signal Sequence and ScramblingSequence

In general, a CSI-RS scrambling sequence may be initialized by a virtualcell ID, and the virtual cell ID may be allocated to CSI-RS resourcesaccording to cell arrangement based on beam or TRP information that maybe included in the virtual cell ID by a gNodeB. Based on the abovedescription, a scrambling ID of 10 bits or more may be used forinitialization of the CSI-RS scrambling sequence and the scrambling IDmay be configured per resource through an RRC message. In addition, slotinformation may be regarded as sequence initialization information forinterference randomization.

Meanwhile, to support UE mobility in a mobile communication system, aneNB may transmit an RS for supporting mobility. For example, the CRS maybe used as a mobility RS in LTE and the CSI-RS may be used as a mobilityRS in the NR system. Here, the eNB may configure a mobility RS using asequence which can be identified per cell or per beam in a cell andtransmit the mobility RS because signal quality is measured per cell orper beam in a cell. For reference, “per cell” will be used to represent“per cell or per beam in a cell” in the following description.

In other words, although a UE requires only information about sequencesof a serving cell in normal data communication, the UE requiresinformation about sequences of all cells when a mobility RS is usedbecause signal quality is measured using mobility RSs of all cells thatthe UE intends to measure. Accordingly, it is possible to configuresequence information about a mobility RS defined per cell and signal thesequence information of the mobility RS per cell to the UE by previouslyconfiguring the sequence information about the mobility RS defined percell or through additional signaling. Then the UE may generate asequence of the mobility RS per cell.

For generation of a mobile RS sequence as described above, acommunication system may define a pseudo-random sequence generator andconfigure different initial values or function input values of thesequence generator for cells, in general. Here, to signal informationrelated to the mobility RS sequence to the UE, an eNB previouslyconfigures information related to an input parameter of a sequencegeneration function per cell and informs the UE of the informationthrough signaling. In the LTE or NR system, a gold sequence is generallydefined by the sequence generator and, when initial values of thesequence generator are changed, sequences generated using differentsequence initial values are delayed with respect to one sequence due tocharacteristics of the gold sequence. That is, when sequences aregenerated using the gold sequence, sequences are generated by beingcyclically shifted by a specific value with respect to one sequence.

Accordingly, the present disclosure proposes a method for solvingprograms caused by such gold sequence property.

That is, a description will be given of a method of generating asequence and mapping the generated sequence to a frequency band in thecases of FIGS. 9 to 11 when a mobility RS sequence is generated on thebasis of the gold sequence according to the above-described method.

1) Case of FIG. 9: If different input values of a sequence generationfunction are provided, sequences generated for respective cellsunconditionally have different values because all cells are located inthe same frequency band. Accordingly, a cell ID is included in the inputvalue of the sequence generation function per cell.

2) Case of FIG. 10: If operation is performed in the same manner as thatof FIG. 9 and generated sequences are mapped to REs/RBs included infrequency bands corresponding to the respective cells in FIG. 10,collision may occur between sequences. That is, different input valuesof a sequence generator are provided and thus cells generate differentsequences in a delayed manner as shown in FIG. 12. However, sequencesmay be mapped in a delayed manner in a sequence mapping procedure, asshown in (1) of FIG. 12, and thus collision may occur between sequences.

To prevent this, a reference bandwidth is determined among a pluralityof system bandwidths, as shown in (2) of FIG. 12, and the referencebandwidth may be defined as resources for starting sequence mapping whensequences are mapped to resources.

According to the above-described method, if a sequence generation ruleis determined and only information about a measurement bandwidth for ameasurement band is acquired, additional information about sequences isnot required because the center frequency of the measurement band isidentical to the center frequency of a system band. LTE is a typicalsystem to which this embodiment is applied.

That is, cell A and cell B define a common reference bandwidth forsequence mapping and use the first RB of the reference bandwidth as amapping reference point of the first sequence bit of all cells.

3) Case of FIG. 11: Distinguished from the case of FIG. 10, cells mayhave different center frequencies as well as bandwidths in the case ofFIG. 11. In this case, even if a reference bandwidth is designated asshown in FIG. 12, a reference point such as a common referenceRE/reference RB cannot be defined because cells have different centerfrequencies and thus a sequence collision problem cannot be solved.

Accordingly, it is necessary to additionally configure a virtualreference position that can be shared by all cells for sequencegeneration and mapping, and the virtual reference position may bedefined in advance by standards or may be determined by a networkincluding an eNB.

Here, the virtual reference position may be a virtual reference REposition or a virtual reference RB position. The virtual referenceposition is called a virtual position because an RB position that is notactually used outside a system band operated by each cell or the currentnetwork is determined as a reference point.

When the virtual reference position is defined in advance by thestandards, a virtual reference RB position determined in thecorresponding frequency band by applying the center frequency of thenetwork on the basis of the maximum number of RBs defined in thestandards may be defined as a reference position for sequence generationand mapping, as mentioned in the case of FIG. 10. Here, the virtualreference RB position may be arbitrarily configured by an eNB in animplementation stage with the number of bits for CSI-RS transmission asa limit.

In addition, it is advantageous to configure the virtual reference RBposition outside the first RB position of a cell having the widestfrequency band in the system band to conserve the number of bits orgeneration of sequences.

Here, distinguished from the case of FIG. 10, cells have differentcenter frequencies as well as different bandwidths in the case of FIG.11, and thus it is necessary to signal how distant a frequency banddefined as a measurement band or a frequency band of an active BWP isfrom a configured virtual reference RB position. To this end, there is amethod of signaling all of information about the virtual reference RBposition, that is, the system bandwidth and center carrier frequency ofa serving cell, and information about a transmission bandwidth perCSI-RS resource and the center frequency of the transmission bandwidthalong with a reference RB (position information of the reference RB)from the system band as the simplest method.

However, if information about the aforementioned virtual reference RBposition is used only for CSI-RS sequence generation and mapping, theinformation about the virtual reference RB position may serve asexcessive overhead.

Accordingly, an eNB may signal, to a UE, only a difference betweenfrequency positions of the virtual reference RB position or virtualreference RE position and a measurement band to be used for actualmeasurement as a sequence offset instead of directly signaling theinformation about the virtual reference position.

The case of FIG. 11 is described in detail with reference to FIG. 13.Referring to FIG. 13, it is assumed that the first RB position in asystem band operated by a network is a virtual reference RB point. Then,a sequence offset with respect to a difference between a reference pointof a measurement band commonly used for all cells and the virtualreference RB point, that is, “sequence offset (1)” is signaled. Here,the reference point of the measurement band may be the first RB or thecenter frequency of the measurement band.

If a UE knows frequency position information about a measurement bandfor an active BWP, a difference between a reference point of the activeBWP and the virtual reference RB point, that is, “sequence offset (2)”may be signaled as a sequence offset. Here, the reference point of theactive BWP may be the first RB or center frequency of the active BWP.

Meanwhile, the sequence offset is commonly applied to CSI-RS resourcesconfigured for neighbor cell measurement.

Here, the unit for the sequence offset may be determined as 1) sequencebit offset (number of bits), 2) the number of RBs or RB groups, 3)sequence bit offset (number of bits)/arbitrary constant, or the like.Here, the arbitrary constant in 2) may be a fixed value or may bedetermined by various RRC configuration parameters such as the bandwidthof an active BWP and RB density of CSI-RS resources.

When a UE receives an input value of a sequence generator for the CSI-RSand sequence offset information from an eNB, the UE may generatesequences using the input value of the sequence generator, derive onlysome of the generated sequences which will be used thereby and use thederived sequences.

For example, when sequences for cell B are generated in FIG. 13,sequences S(d1), S(d1+1) . . . are generated and the UE measures theCSI-RS using only sequences S(d2), S(d2+1) . . . corresponding to ameasurement band among the generated sequences.

Alternatively, the UE may modify the input value of the sequencegenerator using the sequence offset information such that the inputvalue of the sequence generator is delayed by an offset and directlygenerate sequences to be used for measurement. For example, whensequences for cell B are generated in FIG. 13, the user may directlygenerate S(d2), S(d2+1), . . . by modifying the input value of thesequence generator.

Additionally, sequences to be used for measurement may be directlygenerated by generating a mask capable of generating a delay of asequence in the sequence generator and using a corresponding maskingvalue as an additional input parameter of the sequence generator. Forexample, when sequences for cell B are generated, sequences S(d2),S(d2+1), . . . may be directly generated using a masking value capableof providing a sequence offset as an additional input parameter inaddition to the input value of the sequence generator.

The above description is described again. In a broadband componentcarrier (CC) scenario, the CSI-RS shared by UEs may be allocated overthe entire bandwidth. Here, narrowband UEs may perform neighbor cellmeasurement using only some of CSI-RS sequences. Accordingly, it isnecessary to signal additional information about some of CSI-RSsequences to be used for neighbor cell measurement as well asinitialization information of a sequence generator corresponding toinformation for sequence-to-RE mapping. To this end, a referenceposition for sequence-to-RE mapping, that is, an RB position to whichthe first bit generated by the sequence generator is mapped, i.e., areference RB position, needs to be defined.

For example, assuming that a CSI-RS sequence generator is initializedwith cell ID related information for sequence identification, if CSI-RSsequences generated for cells having different bandwidths and centerfrequencies are mapped to RBs within system bandwidths of the cells, twosequences between cells may collide.

Accordingly, to avoid sequence collision, a common reference point forCSI-RS sequence-to-RE mapping between cells needs to be defined, asshown in FIG. 14. Referring to FIG. 14, cells have different systembandwidths and different center frequencies and a reference RB point isconfigured to the first RB position within the whole system bandwidth ofan operator.

Specifically, the following two options may be considered in order todetermine a reference RB point.

Option 1) The reference RB point is configured to the first RE positionof a reference signal within the whole system bandwidth.

Option 2) The reference RB point is configured to a virtual RE position.

Here, option 2 is a method similar to LTE. Here, a reference point isthe first RE of an RS which assumes the maximum number of RBs in RBallocation.

When the center frequency of the system is aligned with a frequency atwhich a UE operates during an initial access procedure and a bandagnostic operation which is the same as a measurement operation usingthe CRS in LTE is required, option 2 is preferable to configure areference RB point.

However, option 2 is not desirable in the NR system because centerfrequency alignment may not be supported. Accordingly, it is desirableto use the first RE position of a reference signal as a reference RBpoint for sequence-to-RE mapping in the whole system bandwidth as inoption 1.

Here, a reference RB is not an actual RB used for transmission performedby cell A which is a serving cell of a target UE and is a virtual RB forsequence-to-RE mapping. In other words, a reference point for sequencegeneration may be commonly configured to the (virtual) first RB in thewhole system bandwidth operated by the network for all neighbor cellsirrespective of the bandwidth of each neighbor cell.

Meanwhile, information about a measurement bandwidth or the position ofan active BWP in the whole system bandwidth needs to be signaled to aUE, and the UE determines a part of CSI-RS sequences used for RSRPmeasurement on the basis of the signaled information. In addition,information about measurement band configuration may include the centerfrequency of the system band of a serving cell, a system bandwidth, thefrequency position of a configured BWP, and the frequency position of ameasurement band in the configured BWP, and the UE may generate CSI-RSsequences using the information about measurement band configuration.However, when the information about measurement band configuration isused only for CSI-RS sequence generation, the amount of redundantlysignaled information increases. That is, there is a disadvantage interms of signaling overhead.

Accordingly, it is possible to signal only a relative distance betweenthe starting RB position of a configured BWP or a measurement bandlocated within the configured BWP and a reference RB position for CSI-RSsequences, that is, an offset between the starting RB position and thereference RB position. In addition, considering that the NR system cansupport various numerologies, the aforementioned RB offset value may beinterpreted on the basis of a specific numerology. Accordingly, it isdesirable that a starting RB offset be represented as a sequence offsetfor sequence generation as shown in FIG. 14.

Candidate values for configuration parameters for CSI-RS-basedmeasurement and signaling methods may be as shown in Table 2.

TABLE 2 Signaling Parameters method Candidate values Periodicity Perfrequency {5 ms, 10 ms, 20 ms, 40 ms} Measurement Per frequency {5-100MHz} for B6G/{50-400 MHz} bandwidth for A6G Sub-carrier Per frequency{15, 30,60 kHz} for B6G/{60, 120 kHz} spacing for A6G Time/Freq. Perresources Symbol position resources Starting RB position, RE density, REposition QCL Per Time reference: PCID {0~1007} information resource/Spatially QCL: SSB ID {0~63} resource group Sequence Per resourceInitialization information: Over 10 bits RE mapping: Sequence offset

CSI-RS-Based Measurement for Cells Which are Not Included in Cell List

When a network configures CSI-RS-based measurement for a plurality ofUEs, the network may provide CSI-RS configuration and a neighbor celllist per resource to the UEs. Here, the neighbor cell list or the numberof CSI-RS resources may be limited in order to reduce signalingoverhead. In addition, to prevent periodic broadcasting of CSI-RSconfiguration, CSI-RS configuration information needs to be providedthrough UE dedicated RRC signaling. When a UE detects an SSB of a cellwhich is not included in the neighbor cell list or does not receiveCSI-RS configuration, the UE may request CSI-RS configuration for thecorresponding cell.

FIG. 15 is a block diagram illustrating components of a transmittingdevice 10 and a receiving device 20 which implement the presentdisclosure.

The transmitting device 10 and the receiving device 20, respectivelyinclude radio frequency (RF) units 13 and 23 which transmit or receiveradio signals carrying information/and or data, signals, and messages,memories 12 and 22 which store various types of information related tocommunication in a wireless communication system, and processors 11 and21 which are operatively coupled with components such as the RF units 13and 23 and the memories 12 and 22, and control the memories 12 and 22and/or the RF units 13 and 23 to perform at least one of the foregoingembodiments of the present disclosure.

The memories 12 and 22 may store programs for processing and control ofthe processors 11 and 21, and temporarily store input/outputinformation. The memories 12 and 22 may be used as buffers.

The processors 11 and 21 generally provide overall control to theoperations of various modules in the transmitting device or thereceiving device. Particularly, the processors 11 and 21 may executevarious control functions to implement the present disclosure. Theprocessors 11 and 21 may be called controllers, microcontrollers,microprocessors, microcomputers, and so on. The processors 11 and 21 maybe achieved by various means, for example, hardware, firmware, software,or a combination thereof In a hardware configuration, the processors 11and 21 may be provided with application specific integrated circuits(ASICs), digital signal processors (DSPs), digital signal processingdevices (DSPDs), programmable logic devices (PLDs), field programmablegate arrays (FPGAs), etc. In a firmware or software configuration,firmware or software may be configured to include a module, a procedure,a function, or the like. The firmware or software configured toimplement the present disclosure may be provided in the processors 11and 21, or may be stored in the memories 12 and 22 and executed by theprocessors 11 and 21.

The processor 11 of the transmitting device 10 performs a predeterminedcoding and modulation on a signal and/or data which is scheduled by theprocessor 11 or a scheduler connected to the processor 11 and will betransmitted to the outside, and then transmits the encoded and modulatedsignal and/or data to the RF unit 13. For example, the processor 11converts a transmission data stream to K layers after demultiplexing,channel encoding, scrambling, modulation, and so on. The encoded datastream is referred to as a codeword, equivalent to a data block providedby the MAC layer, that is, a transport block (TB). One TB is encoded toone codeword, and each codeword is transmitted in the form of one ormore layers to the receiving device. For frequency upconversion, the RFunit 13 may include an oscillator. The RF unit 13 may include N_(t)transmission antennas (N_(t) is a positive integer equal to or greaterthan 1).

The signal process of the receiving device 20 is configured to bereverse to the signal process of the transmitting device 10. The RF unit23 of the receiving device 20 receives a radio signal from thetransmitting device 10 under the control of the processor 21. The RFunit 23 may include N_(r) reception antennas, and recovers a signalreceived through each of the reception antennas to a baseband signal byfrequency downconversion. For the frequency downconversion, the RF unit23 may include an oscillator. The processor 21 may recover the originaldata that the transmitting device 10 intends to transmit by decoding anddemodulating radio signals received through the reception antennas.

Each of the RF units 13 and 23 may include one or more antennas. Theantennas transmit signals processed by the RF units 13 and 23 to theoutside, or receive radio signals from the outside and provide thereceived radio signals to the RF units 13 and 23 under the control ofthe processors 11 and 21 according to an embodiment of the presentdisclosure. An antenna may also be called an antenna port. Each antennamay correspond to one physical antenna or may be configured to be acombination of two or more physical antenna elements. A signaltransmitted from each antenna may not be further decomposed by thereceiving device 20. An RS transmitted in correspondence with acorresponding antenna defines an antenna viewed from the side of thereceiving device 20, and enables the receiving device 20 to performchannel estimation for the antenna, irrespective of whether a channel isa single radio channel from one physical antenna or a composite channelfrom a plurality of physical antenna elements including the antenna.That is, the antenna is defined such that a channel carrying a symbol onthe antenna may be derived from the channel carrying another symbol onthe same antenna. In the case of an RF unit supporting MIMO in whichdata is transmitted and received through a plurality of antennas, the RFunit may be connected to two or more antennas.

In the present disclosure, the RF units 13 and 23 may support receptionBF and transmission BF. For example, the RF units 13 and 23 may beconfigured to perform the exemplary functions described before withreference to FIGS. 5 to 8 in the present disclosure. In addition, the RFunits 13 and 23 may be referred to as transceivers.

In embodiments of the disclosure, a UE operates as the transmittingdevice 10 on UL, and as the receiving device 20 on DL. In theembodiments of the disclosure, the gNB operates as the receiving device20 on UL, and as the transmitting device 10 on DL. Hereinafter, aprocessor, an RF unit, and a memory in a UE are referred to as a UEprocessor, a UE RF unit, and a UE memory, respectively, and a processor,an RF unit, and a memory in a gNB are referred to as a gNB processor, agNB RF unit, and a gNB memory, respectively.

The gNB processor of the present disclosure controls the transceiver totransmit information about a measurement bandwidth for CSI-RSmeasurement and cell list information about a plurality of cells whichare measurement objects and controls the transceiver to map a CSI-RSsequence on the basis of the same reference position configured by ahigher layer and to transmit the CSI-RS sequences to a UE. Then, the gNBprocessor may control the transceiver to receive, from the UE,measurement information about CSI-RS signal strength measured for atleast one of the plurality of cells on the basis of the measurementbandwidth. Here, the first element of the CSI-RS sequence is mapped to asubcarrier corresponding to the configured reference position. Inaddition, the CSI-RS sequence is generated on the basis of a scramblingID configured by a higher layer and the same reference position, and theinformation about the measurement bandwidth includes information on astarting RB of the measurement bandwidth.

The UE processor of the present disclosure may control the transceiverto receive information about a measurement bandwidth and cell listinformation about a plurality of cells and control the transceiver toreceive CSI-RSs of the plurality of cells, to measure reception powerwith respect to the CSI-RSs within the measurement bandwidth and toreport reception power of at least one of the plurality of cells. Here,measurement of the CSI-RSs is performed on the assumption that CSI-RSsequences have been mapped to physical resources on the basis of areference position configured by a higher layer. That is, CSI-RSmeasurement may be performed on the assumption that the first sequenceelement of a CSI-RS is mapped to a subcarrier corresponding to thereference position, and the information about the measurement bandwidthmay include information about a starting RB of the measurementbandwidth.

The gNB processor or the UE processor of the present disclosure may beconfigured to implement the present disclosure in a cell operating in ahigh frequency band at or above 6 GHz in which analog BF or hybrid BF isused.

As described before, a detailed description has been given of preferredembodiments of the present disclosure so that those skilled in the artmay implement and perform the present disclosure. While reference hasbeen made above to the preferred embodiments of the present disclosure,those skilled in the art will understand that various modifications andalterations may be made to the present disclosure within the scope ofthe present disclosure. For example, those skilled in the art may usethe components described in the foregoing embodiments in combination.The above embodiments are therefore to be construed in all aspects asillustrative and not restrictive. The scope of the disclosure should bedetermined by the appended claims and their legal equivalents, not bythe above description, and all changes coming within the meaning andequivalency range of the appended claims are intended to be embracedtherein.

INDUSTRIAL APPLICABILITY

Although the above-described method for transmitting and receiving areference signal and the apparatus therefor have been described based onexamples in which the method and the apparatus are applied to 5G NewRAT,the method and the apparatus are applicable to various wirelesscommunication systems in addition to 5G NewRAT.

What is claimed is:
 1. A method for transmitting a channel stateinformation-reference signal (CSI-RS) by a base station (BS) in awireless communication system, the method comprising: transmittinginformation related to a reference position commonly used for mapping ofCSI-RSs of a plurality of cells; transmitting information related to ameasurement bandwidth for at least one cell among the plurality ofcells; mapping sequence elements for the CSI-RS based on the referenceposition; and transmitting one or more sequence elements for the CSI-RSmapped within the measurement bandwidth among the sequence elements forthe CSI-RS.
 2. The method of claim 1, wherein each first sequenceelement for each of the CSI-RSs of the plurality of cells is mapped to asubcarrier corresponding to the reference position.
 3. The method ofclaim 1, further comprising: receiving information related to receptionpower of the at least one cell.
 4. The method of claim 1, wherein thesequence elements for the CSI-RS are generated based on a scrambling IDof a corresponding cell configured by the higher layer.
 5. The method ofclaim 1, wherein the information related to the measurement bandwidthincludes information related to the starting resource block (RB) of themeasurement bandwidth.
 6. A base station (BS) for transmitting a channelstate information-reference signal (CSI-RS) in a wireless communicationsystem, the BS comprising: at least one transceiver; at least oneprocessor; and at least one computer memory operably connectable to theat least one processor and storing instructions that, when executed,cause the at least one processor to perform operations comprising:transmitting, via the at least one transceiver, information related to areference position commonly used for mapping of CSI-RSs of a pluralityof cells; transmitting, via the at least one transceiver, informationrelated to a measurement bandwidth for at least one cell among theplurality of cells; mapping sequence elements for the CSI-RS based onthe reference position; and transmitting, via the at least onetransceiver, one or more sequence elements for the CSI-RS mapped withinthe measurement bandwidth among the sequence elements for the CSI-RS. 7.The BS of claim 6, wherein each first sequence element for each of theCSI-RSs of the plurality of cells is mapped to a subcarriercorresponding to the reference position.
 8. The BS of claim 6, theoperations further comprising: receiving information related toreception power of at least one cell.
 9. The BS of claim 6, wherein thesequence elements for the CSI-RS are generated based on a scrambling IDof a corresponding cell configured by the higher layer.
 10. The BS ofclaim 6, wherein the information related to the measurement bandwidthincludes information related to the starting resource block (RB) of themeasurement bandwidth.
 11. At least one computer memory storinginstructions that, when executed, cause at least one processor tocontrol a base station (BS) in a wireless communication system toperform operations comprising: transmitting information related to areference position commonly used for mapping of a channel stateinformation-reference signals (CSI-RSs) of a plurality of cells;transmitting information related to a measurement bandwidth for at leastone cell among the plurality of cells; mapping sequence elements for theCSI-RS based on the reference position; and transmitting one or moresequence elements for the CSI-RS mapped within the measurement bandwidthamong the sequence elements for the CSI-RS.